Telephone-exchange system



May 6, 1930; E. G, WRiGHT T AL l,757,446

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TELEPHONE EXCHANGE SYSTEM Filed May 10, 1928 17 Sheets-Sheet 14 @Y JM E.P. G. WRIGHT ET AL 1,757,446

TELEPHONE EXCHANGE SYSTEM Filed May l0, 1928 v17' Sheets-Sheet 15 JpH/vf. 15A/fm AMA/v /1 EAMERUA/ May 6, 1930.

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May 6, 1930. E, P, G, wRlGHT ET AL 1,757,446

TELEPHONE EXCHANGE SYSTEM Filed May 1o, 1928 1'? sheets-sheet 1'? ESMONDG. WR/GHI /A/f/ENTo/.' JH/V /7f 5,4 /fE/i.

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ATTO/MQW Patented May 6, 1930 STATES EBMCND P. WRIGHT, F CROYDON, .TURNH. E. BAKER, 0F HAHPSTEAD, AND ALAN H. CAMERON, 0F BRONDESB'UBY,ENGLAND, ASSIGNOBS T0 WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEWYORK, N. Y., A CORPCBATION OF NEW YORK TEEPHONEEXCHANGE SYSTEMApplication led Hay 10, 1928, Serial No. 276,734, and in Great Britainlay 10, 1927 This invention relates to telephone exchange systems andmore particularly to systems of the character in` which' connections areextended between subscribers lines by 's means of machine switchingapparatus under the control of common register senders. The invention isespecially adapted for use in large multi-ofceexchange areas and theobject thereof is to provide a system of simple lo character whichutilizes all apparatus involved to the most economical degree and withthe greatest surety of operation.

In the prior art, systems employing power driven switches of the panelor rotary type controlled by common register senders, and systemsemploying switches of the Strowger or step-by-step type controlled byso-called directors, have been disclosed for use in large multi-officeexchange areas. The syszo tem of the present invention has been designed particularly to simplify the connection extending selectors andthe equipment of the common register senders to order that lessapparatus may be required for maintaining adequate service and in orderthat the cost of maintenance may be reduced as much as possible.

In the embodiment of the invention disclosed herein by way ofillustration, all switches employed in the exchange are of the singlemotion rotary type movable in one direction only. The calling lines areassociable with' a first group selector by means of groups of linkcircuits each link circuit comprising a line finder and -a selectorfinder. Each link circuit has access through its selector finder to agroup of rst selectors havin access in turn to a single register sender.ssociated with a group of link circuits is a distributor switch.Provision is made whereby, upon the initiation of a call in a group ofcalling lines, the distributor switch will select only an idle link, theselector finder of which has access to an idle first group selector in agroup having access to an idle register sender. A single register senderis multipled directly before all first group selector trunks of aselector group and may be associated with anyone of the group selectortrunks, no hunting :for an idle sender being required other than thehunting o eration of the link l'distributor switch, w ereby time issaved in associatin an idle sender with a calling line and additionalswitches are obviated.

The selector switches of each switching sta e except the rst,`aredivided into groups an a minor or auxiliary switch is rovided common tothe selectors of each suc group. The minor switches are directed b imvulses transmitted thereto over the estab ishe connection from thecommon sender and mark the groups of terminals, and in the case of thefinal selector the desired line terminal to which their associatedselectors shall hunt. The selector switches therefore have no directedmovement but only a single hunting movement to findV a terminal in the,group marked by the minor switch. The rst group selector is not providedwith a minor switch but hunts to find an idle trunk in a group markeddirectly by the sender. Provision is also made that when a groupselector hunts twice over its bank without finding an idle trunk in thegroup marked or the nal selector hunts to the terminal of the markedwanted line and inds the line busy, all switches beyond the first groupselector are released, the finder is dismissed,` and a busy signal istransmitted from the first group selector to the calling line.

The minor switches may be made small and compactand therefore readilyresponsive to impulses transmitted thereto from the register sender.Further, since only one minor switch and the control relays therefor isrequired for a group of selectors, and the structure of the selector isextremely simple, only a rotary magnet and testing relay beingnecessary, an appreciable economy in equipment is realized. In additionsince all selectors and minor switches are ofthe rotary single motiontype, they may be mounted on hinged panels to either side of themounting frame whereby, they may be swung out to enable ready accesstothe cable connections extendincr thereto. By this arrangement anapprecia le saving in mountin space is attained.

Connections between o ces of the exchan e area are extended overtwo-wire ofiice trun s and provision is made at the outgoing ends ofsuch trunks to mark an entire group busy if the minor switch and controlrelays common to the incoming selectors in which the distant ends of thetrunks terminate is unavailable. This busy condition is controlled overthe two-wire trunks of the group without the additional use of extraconductors in the inter-office cable.

The common register-sender for controlling the setting of the minorswitches is provided with a group of four registers which respond toimpulses dialed by calling subscribers. The first two office code seriesof impulses are registered on two of these registers and are thentransferred to translator switches. The third office code series ofimpulses is registered directly on one of the translator switches.Following the transfer of the code registrations to the translators theregisters upon which they were initially registered are restored and arelater employed, together with the two other registers, to register thenumerical digits of the wantedline number. As soon as the ofiice codehas been completely registered the sender proceeds to transmit series ofimpulses for extending the connection from the calling line to theoffice in which the wanted line terminates. For this purpose a sendingswitch is employed which assumes a plurality of settings as directedsuccessively from a plurality of banks of one or the other of thetranslators,lterminals of the sending switch being multipled to pointsin the banks of the translators with resistances interpo` lated betweensuch contact points. The arrangement is such that when the sendingswitch has advanced to the point marked by a translator bank thedirection of current f'low through a relay will be reversed to mark theend of the selecting stage. There tht` code registered 0n a translatorindicates that the connection must be extended through more than threeselecting stages to reach the desired oiiice the translator is advancedone step following the completion of selections controlled through thethree stages and in its advanced position controls selections throughthree additional stages.

In order that the apparatus ofthe exchange may at all times bemaintained in proper con dition for rendering efficient service aroutine test circuit is provided for association with the common minorswitches and control circuits serving groups of selectors at anyswitching stage. This test circuit may, at the option of an attendant,be rendered effective and will continue as long as desired to selectidle minor switch control circuits and to test their operation,operating suitable alarm signals when any such circuit is found tofunction improperly.

Provision is also made for automatically hunting for any line of anoffice on which a calling condition exists for more than a predeterminedperiod without the establishment of a connection, such a. conditionarising through a permanent abnormal ground on the calling line orthrough the neglect of the calling subscriber to dial a number afterlnitiating a call. When such a line is thus selected the number thereofis displayed on an indicator.

A clearer understanding of the invention will be obtained from aconsideration of the following detailed description in connection withthe drawings in which:

Fig. 1 shows a link circuit and preselecting arrangement;

Fig. 2 shows a portion of the first group selector;

Fig. 3 shows the remainder of the first group selector and a portion ofthe sender;

Figs. 4, 5, 6, 7 and 8 show the remainder of the sender; 4

Fig. 9 shows a second group selector;

Fig. 10 shows a testing arrangement for testing the control equipment ofthe group selector shown in Fig. 9;

Fig. 11 lshows a relay arrangement for the outgoing end of a two-wireinter-office trunk;

Fig. 12 shows a selector at the incoming end of a two-wire trunk;

Fig. 13 shows a final selector;

Fig. 14 shows the common control equipment for the selector of Fig. 13;

Fig. 15 shows an arrangement for selecting and identifying a callingline on which a permanent signal condition exists;

Figs. 16 and 17 show a final selector and control equipment forconnecting with private branch exchanges; and

Fig. 18 shows the manner in which the remaining figures should bearranged.

A brief summary of the operation of the system as a whole will first begiven.` The initiation of a call by a subscriber at substation 101causes distributor switch 130 to hunt for a link circuit having access.to a group of first group selectors served by a register sender which isidle. When such a link circuit, forexample link 100, has been found theselector finder 120 is operated to find an idle selector in the group.The line finder 110 is then operated to connect the calling line to theselector and the distributor switch is advanced to the next link. Whenthe calling line is connected through. the sender is associatedtherewith and with the selector by means of relay 203. There is such arelay for each first group selector and the sender is connected inmultiple to the contacts of such relays in all of the selectors which itserves.

The called line designation is then recorded in the sender. The firstdigit of the office code is recorded on register 52() and transferred totranslator 600. The second digit y is recorded on register 510 andtransferred to translator G50. The third digit is recorded directly ontranslator 600. Registers 520 and 510 are then restored to normal andthe numerical digits are recorded on registers 540,530, 520 and' 510 insuccession.

Immediately following the reception of the third digit the sendingswitch 850 is actuated. A distributing rack `810 is provided comprisinga plurality of resistances 811 to 823 connected between battery andground. The normal terminal of brush 854 of the sendlo ing switch isconnected to ground and the succeeding terminals are connected to thedistributing rack at points between succeeding resistances. Theterminals of brushes 602, 603 and 604 of translator 600 and brushes 654,653 and 652 of translator 650 are cross connected to distributing rack810 in accordance with the routing corresponding tothe setting of thetranslator. A circuit is established including brush 854 and translator2g b rush 602, or 652 according to which translator is effective andswitch '850 is advanced under the control of an interrupter until brush854 reaches a. terminal beyond that connected to the point marked by thetranslator setting so that the direction of current flow in the circuitis reversed. When this occurs relay 708 which is included in thiscircuit is operated, stopping the sending switch andpreparing thecircuit for the next selection. Due to the intimate relation between thesender and the first group selector the sending switch 850 is itselfemployed as the minor switch for that selector and the setting `01E thesending switch marks the group ot' terminals within which selector 300is to hunt. Due to the large number of trunks outgoing Vfrom a firstgroup selector, this selector made up of two, or possibly more switchstructures,with two operating magnets 301 and 302 and two testrelays 209and 210. while discrimination between the switches is made by thesetting of the sending switch.

When the first group selector has been positioned, the sending switchbecomes effective to control the sending out of impulses to the secondgroup selector. Minor switch 910 is positioned in response to theseimpulses and marks a group of terminals over which the second grouplselector 900 hunts. Translator 600 provides for three selections whiletranslator,650 provides for as many as six selections in order to pick agroup of trunk outgoing to a desired oliice. Only two selectors havebeen shown, it being assumed that subsequent selectors would beessentially duplicates of the second group selector 900.'

The first numerical digit controls the setting of minor switch 1210whereupon switch 1200, is operated to select an intermediate b selectorwhich is not shown. This intermediate selector in turn picks a finalselector. Two types of final selectors may be employed, that shown inFigs. 13 and 14 serving indi- .vidual lines. The minor switch. 1400 ispo sitioned once for the tens digit after which the final selector huntsfor the group of ten lines marked b the minor switch. The minor switchis t en restored and re-operated in response to the units digit and theinalV selector hunts for the called line so marked. The final selectorshown in Figs.'16 and 17 will ,serve either individual lines or groupsof .to a private branch exchange the final selector first hunts for theterminal marked by the minor switch 1710 and then hunts for an I idlebranch exchange trunk. The final selector applies ringing current to thewanted line and completes the connection.

The operation ofthe circuits will now be discusse in more detail. Owingto thelarge number of contacts controlled by certain relays, thesecontacts will be referred to according to their numerical positioncounting from the relay out. 'For example, the innermost contact ofrelay203vwill be called the 1st front contact .of that relay and theoutermost contact will be called the 12th front contact. Only singlemotion rotary switches are employed as pointed out above. Three types ofswitches may be distinguished depending on the number of terminals towhich each brush has access. For example, the selector switches and thetranslators have 100 sets of terminals each; the register switches andminor switches have 11 sets of terminals, while the sending switchconstitutes a class by itself having 25 sets of terminals.

When the subscriber at substation 101 initiates a call by removing hisreceiver from the switchhook he completes a circuit from battery throughthe winding of line relay 102, outer left back contact of relay 103,over the substation circuit, back to ground at the inner left backcontact of relay 103. Relay 102 in operating` connects ground toconductor 125 for initiating the extension of the line to an idle firstgroup selector. 1t also connects battery through the Winding of relay103, and in parallel therewith through resistance 132 and the right backcontact-oitl relay 103, to terminal 117 to identify the calling line tothe line finder 110. Y

The connection of ground to conductor 125 completes a circuit over theouter right ack contact of relay 122, conductor 133, winding of relay104to battery. Relay 104 in operating prepares a circuit from batterythrough the right winding of relay 105, right frontcontact of relay 104to brush106 to test the link circuits for availability. It alsocompletes a circuit from battery through uit

